Chrome, cobalt complex salt thiol nickel complexes, anthraquinone derivatives and the like are known in the prior art as near infrared ray absorbable, light transmitting materials. Also known is a solar radiation reflecting film in which aluminum, copper or the like metal is vacuum-deposited on one surface of a polyethylene terephthalate film. Since such an infrared rays reflecting film well transmits visible rays but reflects near infrared--infrared rays, when applied to a glass of window or the like opening part of buildings, it exerts daylight controlling and heat insulating effects by reflecting solar radiation of the sun light or heat radiation from the interior of the room, keeping its transparency. Transparent, thermal insulation films having such characteristics are applied to windows of buildings, freezer-refrigerator show cases, thermal insulating surfaces, car windows and the like and useful for example in improving dwelling environment and saving energy.
However, solar radiation blocking materials of the prior art, when made solely of organic materials, have a disadvantage in that their initial properties are deteriorated as the environmental conditions change or with the lapse of time, due to their poor durability (weather resistance or the like). On the other hand, those which are made of complex materials have good durability, but they not only absorb rays of near infrared region spectra but also absorb visible region spectra and the compounds themselves are strongly colored, and thus their applications are limited.
Also, solar radiation reflecting films of the prior art reflect not only infrared rays but also visible rays by the metal deposited, thus posing a fatal disadvantage in that the interior of a room becomes dark when they are applied to window glass and the like. In addition, since a large apparatus is necessary to form such a deposited layer of metals, their production cost becomes high and their general use as final products therefore becomes limited.
In order to form a layer or coat of solar radiation absorbents, the solar radiation absorbing agents must be uniformly dispersed in resins. As binders of the resin, acrylic resin, polyester resin, alkyd resin, polyurethane resin, epoxy resin, amino resin, vinyl resin or the like thermoplastic resins are generally used. However, these resins to be used as the binder are apt to get flaws due to poor scratch resistance of the coated layer. In order to improve scratch resistance of these films to a practical level, it is desirable to carry out a hard coating treatment on the outer surface of reflecting film. However, such a process in which a solar radiation absorbing material is coated and then its outer surface is again subjected to hard coating leads to higher cost and poorer general use.